The percent by volume of unfrozen, liquid, ice cream mixture by which the finished ice cream has increased during freezing due to the incorporation of air. Most bulk half-gallons from supermarkets are about 100% overrun (half air). Herrell's is much lower than that. A low-overrun ice cream is richer, creamier, lingers longer in the mouth, is more filling, melts more slowly, stands up better to hot fudge and soda water, and makes for thicker milkshakes (frappes).